Preheat the oven to 350 F and prepare a 7x11 inch baking dish with non-stick spray and then set it aside.
Place the butter, brown sugar and cinnamon into a small pot over medium heat. Stir and cook for 2-3 minutes and the butter has completely melted and then pour the mixture into the bottom of the baking dish. Arrange the banana slices in the dish (cut side down) and then set it aside.
Prepare your cake by stirring together flour, sugar, baking soda and sea salt in a mixing bowl then set it aside. In another bowl, whisk together the eggs, coconut oil, almond milk, vanilla and vinegar until combined. Add the wet ingredients to the dry and stir until combined. Pour the batter evenly over the bananas. Bake for 28-32 minutes and toothpick comes out clean when inserted into the center. Let the cake cool for 15 minutes before serving warm or let it cool completely and serve the cake at room temperature.
Store the cake in an airtight container in the refrigerator for up to 3 days.